1. Field of the Invention
The present invention relates to an optical fiber, and more particularly to a low bend loss optical fiber.
2. Description of the Related Art
As an FTTH (Fiber To The Home) subscriber transmission service network of 100 Mbps or more has been recently built, and the related service industries have been activated, the demand for an optical fiber with an enhanced bend resistance for broadband transmission is rapidly increased.
A general passive optical network (PON) for building FTTH includes an optical line terminal (OLT) positioned at the side of a central office (CO), an optical network unit (ONU) or an optical network termination (ONT) positioned at a user home apparatus or around the apparatus, and a remote node (RN) provided with a splitter or a wavelength division multiplexer (WDM) for connecting these in a tree topology. The CO and the RN, and the RN and the multiple ONUs are generally interconnected by a low water peak fiber (LWPF; a broadband transmission optical fiber). Also, by using a lead-in optical cable, a feeder point, such as an electric pole, is connected to the home lead-in hole. Herein, as the lead-in optical cable, a bending insensitive fiber with an enhanced bend resistance appropriate for the installation indoor/outdoor is mainly used. In actuality, compared to general optical characteristics (such as loss, and dispersion), the installation, and the bend loss occurring by a physical external force in the field using an optical fiber are main factors in largely restricting home network construction. When such a bend loss property is worsened, a problem may be caused in the optical loss and data transmission.
As described above, communications networks using optical fibers have an advantage in that a large amount of data can be transmitted at a high speed in a short period. Meanwhile, the communications networks have a problem in that optical fibers are damaged due to external physical force, and optical loss and a problem of data transmission can occur because of the damage to the optical fibers.
Optical fibers, which include a core and a clad, which has a refractive index significantly different from that of the core and is disposed around the core so that optical loss due to physical force, such as bending, etc., is minimized, is known in the art. There are disclosed the above described type optical fibers, including holey optical fibers manufactured by companies, such as Sumitomo, NTT, etc, or optical fibers having a fine bubble nano structure manufactured by Corning corp., or optical fibers, which have a ring trench clad refractive index profile and are manufactured by for example OFS.
The holey optical fibers are excellent in view of the bending loss. However, they have a problem in that they require high manufacturing cost due to a complicated manufacturing process. Further, it is difficult to connect the holey optical fibers with typical optical fibers of G652 standards, and the holey optical fibers have large optical loss. Also, optical fibers manufactured by Corning corp. have problems with regard to mechanical strength, splicing loss, and a difficult splicing method, which may be caused by a fine bubble nano structure.
However, conventional optical fibers with a ring-trench clad structure have a stable structure and relatively superior characteristics, such as splicing loss, mechanical strength, etc in comparison with the above-described optical fibers. However, there is a problem in that the conventional optical fibers have comparatively inferior optical characteristics in optical loss due to bending.